1. Field of the Invention
The present invention relates generally to computer communications, and more particularly to methods and systems for providing effective short-range communication using electric fields.
2. Description of the Related Art
The concept of using a personal area network (PAN) as a medium for short range communication using a person""s interaction with an electric field is discussed in U.S. Pat. No. 5,796,827, entitled System and Method for Near-Field Human-Body Coupling for Encrypted Communication with Identification Cards, owned by the same assignee as is the present invention and incorporated herein by reference. As disclosed in the above-mentioned patent, using the principles of PAN a small, lightweight transmitter is incorporated in a personal security card that is about the size of a credit card and that can be worn or otherwise carried by a person. The PAN transmitter automatically communicates information (for example, the person""s identity, personal identification number (PIN), social security number, security clearance, and so on) to a PAN receiver via an electric field with which the person interacts. According to PAN principles, the receiver is associated with a computer that is positioned nearby the location of the person, such that the PAN transmitter communicates with the computer.
Owing to the principles underlying PAN communications, the PAN receivers are low power, low latency, low cost receivers that can be easily disposed on, e.g., a computer, computer mouse, keyboard, or security reader in a room. The receivers sense signals that are sent by the transmitter and that are coupled through the person""s body. As mentioned above, these signals carry information, such as authenticating information indicating that the bearer of the transmitter is authorized to use a particular computer or enter a particular area, or that the bearer of the transmitter was present in a particular room at a particular time.
With the above in mind, it will be appreciated that many potential applications for PAN communication exist. Among the myriad applications of PAN communication systems is ensuring that only a person carrying a valid PAN transmitter can log on to a particular computer or computer system. Further applications include authenticating a person who desires to enter a restricted access area, or otherwise monitor the movement of people in a building, so that their whereabouts are known. Still further, PAN communication can be used to grant selective access to automatic teller machines (ATMs). All of the above applications, owing to the nature of PAN communication, require a person to do nothing other than bear a valid PAN transmitter. Thus, PAN communication systems are efficient and convenient solutions for a wide range of personal authentication nuisances.
As recognized by the present invention, while PAN systems are proven, highly effective communication systems, it happens that in certain applications PAN system performance can be further optimized. For example, when a person carrying a valid PAN transmitter wishes to access a computer having a PAN receiver mounted in the keyboard of the computer, the transmitted signal can be undesirably significantly attenuated when the user places his hands or arms on the keyboard. Still further, the present invention recognizes that undesirable coupling and shunting can occur between PAN receivers and a metal surface on which the receivers are supported. Moreover, the present invention recognizes that the signal strength from a PAN transmitter can be undesirably affected when the transmitter is carried in, for example, a person""s pocket along with other metal objects such as metal coins. And, the present invention recognizes that unauthorized third persons might position themselves between a person carrying a valid PAN transmitter and a receiver to undesirably gain access to a computer or room that is associated with the PAN receiver. For example, the present invention recognizes that a signal from a PAN transmitter might be coupled to a PAN receiver of an ATM machine or a computer-controlled subway turnstile through a person who has interposed herself between a valid PAN transmitter and the receiver, thereby affording the person unauthorized access to the ATM machine or turnstile.
Fortunately, the present invention recognizes that it is possible to overcome the above-noted problems efficiently and effectively.
A personal area network (PAN) communication system includes a portable PAN transmitter, a computer, and more than one PAN receiver antenna associated with the computer such that communication can be established between the PAN transmitter and the computer. In accordance with PAN principles, communication between the transmitter and computer is established using an electric field.
In a preferred embodiment, a data input device such as a keyboard communicates with the computer, and the receiver antennae are mounted on the data input device. The system includes at least three, and preferably four, receiver antennae. At least one of the receiver antennae extends substantially from the left side to the right side of the keyboard.
As disclosed in detail below, the receiver antennae are associated with a receiver and the receiver is associated with a signal. With this in mind, the preferred system further includes logic means for selecting one or a combination of multiple antennas to produce a maximum received signal. In this way, an optimum combination of the receiver antennae is established by decoupling those antennae that might be shielded from, or otherwise attenuated from, the transmitter by, e.g., the person""s arms.
In another aspect, a PAN communication system is disclosed that communicates information via an electric field from a PAN transmitter to a PAN receiver. The PAN receiver includes at least one receive electrode disposed above a driven shield. Furthermore, an insulator layer is sandwiched between the receive electrode and the driven shield. A buffer, such as a unity gain amplifier, is electrically connected to the driven shield and to the receiver. The driven shield, substantially electrically isolates the receive electrode from any or other grounding source in the vicinity of the receive electrode, increasing the impedance and lowering the capacitance of the receive electrode.
In still another aspect, in a PAN communication system, a PAN transmitter is disclosed. The transmitter includes plural transmitter electrodes. In a particularly preferred embodiment, the transmitter includes first and second driven electrodes, with each driven electrode being energized by a respective buffer circuit and with each buffer circuit being electrically connected to a signal source.
In yet another aspect, a PAN communication system includes at least one PAN receiver including differential receive electrodes and at least one portable PAN transmitter. Per present principles, the receive electrodes are positioned to measure the electrical potential difference across a person, whereby a person carrying a PAN transmitter will produce a substantial measured potential across the receive electrodes, while a person who does not have a PAN card on their person will produce substantially no electric potential across the receive electrodes. This prevents communication from the PAN transmitter to the receiver via a person without a PAN card.
Preferably, when a receive electrode is placed near the ground or other electrical body which may shunt, conduct, or otherwise reduce the received signal, a guard electrode is juxtaposed with and insulated from the receive electrode. Additionally, a guard driving follower amplifier is electrically connected from the receive electrode to the guarded electrode, to electrically isolate the receive electrode from the ground or electrical body.
In another aspect, a communication system for communicating data between a portable transmitter and a computer system nearby the transmitter using an electric field affected by a person bearing the transmitter includes a receiver that in turn includes plural receiver antennae. The receiver antennae are associated with the computer system such that at least some electric field lines from the person are not shunted away from at least one of the receiver antennae when the person moves an arm toward the computer system.
In yet another aspect, a communication system includes a receive electrode disposed above a metal surface and a driven shield disposed between the receive electrode and the metal surface to shield the receive electrode from the metal surface.
In still another aspect, the communication system includes an electrostatic transmitter including multiple driven electrodes, electrically isolated from at least one reference electrode.
In another aspect, a communication system includes a computer, an electrostatic receiver associated with the computer, and at least one receive electrode electrically connected to the receiver. A portable electrostatic transmitter is bearable by a first person for communicating with the computer via the receiver. Per the present invention, means are provided for preventing communication between the transmitter and receiver when a second person not bearing an electrostatic transmitter is interposed between the transmitter and the receiver. In one embodiment, the means for preventing includes a detector for detecting a predetermined characteristic in the signal when a first person bearing the transmitter moves a limb toward the receive electrode. In a particularly preferred embodiment, the predetermined characteristic is at least one of: an amplitude minimum, and a change of phase.
The invention can also include a general purpose computer programmed according to the inventive steps herein to dynamically determine an optimum combination of PAN receive electrodes that are associated with a PAN receiver system. The invention can also be embodied as an article of manufacturexe2x80x94a machine componentxe2x80x94that is used by a digital processing apparatus and which tangibly embodies a program of instructions that are executable by the digital processing apparatus to undertake the present invention. This invention is realized in a critical machine component that causes a digital processing apparatus to perform the inventive method steps herein.
The details of the present invention, both as to its structure and operation, can best be understood in reference to the accompanying drawings, in which like reference numerals refer to like parts, and in which: